In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, LTE (Long-Term Evolution) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. In an LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. With the UMTS network, successor systems of the LTE system are also under study for the purpose of achieving further broadbandization and higher speed (referred to as, for example, “LTE-advanced” or “LTE-enhancement” (hereinafter referred to as “LTE-A”)).
In the downlink of the LTE system (for example, Rel. 8), CRSs (Cell-specific Reference Signals), which are associated with cell IDs, are defined. These CRSs are used to demodulate user data, and, in addition, used to measure downlink channel quality (CQI: Channel Quality Indicator) for scheduling and adaptive control, and so on. In the downlink of successor systems of LTE (for example, Rel. 10), CSI-RSs (Channel State Information-Reference Signals) are under study for dedicated use for CSI (Channel State Information) measurements.